ci: remove unused matrix argument vtk-tag

Author: AlexyPellegrini

.github/workflows/ci.yml

@@ -10,7 +10,6 @@ jobs:
       fail-fast: true
       matrix:
         os: [ubuntu-latest, windows-latest, macos-15]
-        vtk-tag: ["9.6.0"]
         py-abi: ["cp310"]
         include:
           # Python version to install on host